The present inventions relate to grids for use in batteries (e.g., lead-acid batteries such as batteries for vehicle starting, lighting, and ignition applications; marine batteries; commercial batteries; industrial batteries; batteries for use with hybrid-electric vehicles; etc.). More specifically, the present inventions relate to grids that have a configuration which resists shorting of a battery cell due to growth of the grids.
Lead-acid batteries conventionally include a number of cells in which energy is stored. For example, a 12 volt battery may include six cells, each of which provides 2 volts. Each of the cells includes one or more positive electrodes or plates and one or more negative electrodes or plates. An electrolyte (e.g., acid such as dilute sulfuric acid) is also provided in the cells to facilitate chemical reactions which take place in the cells during charging and discharging of the battery.
The positive and negative electrodes each comprise a grid made from lead or a lead alloy (e.g., a lead-calcium alloy) on which an active material in the form of a paste is provided. Such grids include a plurality of wires coupled to a plurality of nodes (e.g., a battery grid may include a frame comprising four sides with a lug or current collector extending from one of the sides and a network of wires or grid elements interconnected with a plurality of nodes).
The positive and negative electrodes are arranged in each of the cells in alternating fashion and are separated from adjacent plates by a separator (e.g., a microporous polymeric separator). For example, the negative electrodes may be contained within a separator envelope to electrically isolate them from adjacent positive electrodes. In this manner, the positive and negative electrodes are prevented from coming into direct contact with each other, which would cause a short in the cell.
Over an extended period of use, the grids will corrode, which in turn will cause the grids to grow. By way of illustration, FIG. 1 shows a cell having a first electrode 10 (e.g., a positive electrode) with a current collector 12 arranged adjacent a second electrode (e.g., a negative electrode, partially obscured by electrode 10 in FIG. 1) with a current collector 22. The current collector 12 of the positive electrode is electrically coupled to other positive electrodes in the cell by a strap or connector 14, while the current collector 22 of the negative electrode is electrically coupled to other negative electrodes in the cell by a strap or connector 24. The positive strap in a cell is then connected to a negative strap in the next cell.
Growth of positive electrode 10 is illustrated by dashed lines 30 and 32. When installed in a battery container, the grids are generally constrained on their sides and bottom by walls of the battery container. Accordingly, growth of the grids generally occurs along the top surface of the grids. In certain situations, such unconstrained growth in the positive vertical direction may cause a short of the cell. For example, as shown in FIG. 1, the growth of the positive grid illustrated by dashed line 32 results in a portion of the grid coming into contact with strap 24 that is connected to the negative electrodes. In such a situation, the positive and negative electrodes are electrically coupled together, which may act to short the cell. Thus, while adjacent positive and negative electrodes may be separated from each other with a polymeric separator, shorting may still occur due to corrosion of the grids which causes growth in the vertical direction.
While it is known to provide grids for use in batteries, such known grid configurations do not provide certain advantageous features and/or combinations of features.